diff options
| -rw-r--r-- | .topdeps | 2 | ||||
| -rw-r--r-- | .topmsg | 72 | ||||
| -rw-r--r-- | hurd/hurdsig.c | 3 |
3 files changed, 6 insertions, 71 deletions
@@ -1 +1 @@ -t/hurdsig-fixes +t/hurdsig-global-dispositions @@ -1,70 +1,4 @@ -Subject: [PATCH] Global signal dispositions. +2012-09-05 Richard Braun <rbraun@sceen.net> -Although they should not change the -default behaviors of signals for cthread programs, these patches add -new functions which can be used by libpthread to enable -POSIX-conforming behavior of signals on a per-thread basis. - -YYYY-MM-DD Jeremie Koenig <jk@jk.fr.eu.org> - - e407ae3 Hurd signals: implement global signal dispositions - 38eb4b3 Hurd signals: provide a sigstate destructor - 344dfd6 Hurd signals: fix sigwait() for global signals - fb055f2 Hurd signals: fix global untraced signals. - -YYYY-MM-DD Thomas Schwinge <thomas@codesourcery.com> - - * sysdeps/mach/hurd/fork.c (__fork): In the child, reinitialize - the global sigstate's lock. - -This is work in progress. - -This cures an issue that would very rarely cause a deadlock in the child -in fork, tries to unlock ss' critical section lock at the end of fork. -This will typically (always?) be observed in /bin/sh, which is not -surprising as that is the foremost caller of fork. - -To reproduce an intermediate state, add an endless loop if -_hurd_global_sigstate is locked after __proc_dostop (cast through -volatile); that is, while still being in the fork's parent process. - -When that triggers (use the libtool testsuite), the signal thread has -already locked ss (which is _hurd_global_sigstate), and is stuck at -hurdsig.c:685 in post_signal, trying to lock _hurd_siglock (which the -main thread already has locked and keeps locked until after -__task_create). This is the case that ss->thread == MACH_PORT_NULL, that -is, a global signal. In the main thread, between __proc_dostop and -__task_create is the __thread_abort call on the signal thread which would -abort any current kernel operation (but leave ss locked). Later in fork, -in the parent, when _hurd_siglock is unlocked in fork, the parent's -signal thread can proceed and will unlock eventually the global sigstate. -In the client, _hurd_siglock will likewise be unlocked, but the global -sigstate never will be, as the client's signal thread has been configured -to restart execution from _hurd_msgport_receive. Thus, when the child -tries to unlock ss' critical section lock at the end of fork, it will -first lock the global sigstate, will spin trying to lock it, which can -never be successful, and we get our deadlock. - -Options seem to be: - - * Move the locking of _hurd_siglock earlier in post_signal -- but that - may generally impact performance, if this locking isn't generally - needed anyway? - - On the other hand, would it actually make sense to wait here until we - are not any longer in a critical section (which is meant to disable - signal delivery anway (but not for preempted signals?))? - - * Clear the global sigstate in the fork's child with the rationale that - we're anyway restarting the signal thread from a clean state. This - has now been implemented. - -Why has this problem not been observed before Jérémie's patches? (Or has -it? Perhaps even more rarely?) In _S_msg_sig_post, the signal is now -posted to a *global receiver thread*, whereas previously it was posted to -the *designated signal-receiving thread*. The latter one was in a -critical section in fork, so didn't try to handle the signal until after -leaving the critical section? (Not completely analyzed and verified.) - -Another question is what the signal is that is being received -during/around the time __proc_dostop executes. + * hurd/hurdsig.c (sigstate_is_global_rcv): Do not return true + if _HURD_GLOBAL_SIGSTATE is null. diff --git a/hurd/hurdsig.c b/hurd/hurdsig.c index 44605058f2..88158d920c 100644 --- a/hurd/hurdsig.c +++ b/hurd/hurdsig.c @@ -162,7 +162,8 @@ _hurd_sigstate_set_global_rcv (struct hurd_sigstate *ss) static int sigstate_is_global_rcv (const struct hurd_sigstate *ss) { - return ss->actions[0].sa_handler == SIG_IGN; + return (_hurd_global_sigstate != NULL) + && (ss->actions[0].sa_handler == SIG_IGN); } /* Lock/unlock a hurd_sigstate structure. If the accessors below require |